The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
When an internal combustion engine is initially started, the engine and an exhaust system of the engine are cold. The low temperature makes it difficult for fuel to vaporize in the cylinders. Incompletely vaporized fuel is not completely combusted. A portion of fuel that is not completely combusted at start-up increases hydrocarbon (HC) and carbon monoxide (CO) levels in the exhaust.
Vehicles that include the internal combustion engine may also include a catalytic converter to treat the exhaust. The catalytic converter includes a catalyst that catalyzes the oxidation of HC and CO as well as the reduction of nitrogen oxides in the exhaust. The catalyst does not efficiently control emissions at start-up because: 1) a higher fraction of fuel remains unburned and is subsequently exhausted, and 2) the catalyst is not sufficiently hot.
The catalyst operates efficiently when it reaches an operating temperature referred to as a light-off temperature. The catalyst reaches the light-off temperature after the engine and the exhaust system have been adequately heated from engine operation. During a cold start, engine speed is elevated and spark timing is retarded to increase exhaust temperature and exhaust flow to quickly heat the catalyst.
An engine control module implements on-board diagnostics (OBD) to ensure compliance with emission limits during a cold start. OBD may monitor the engine and exhaust system components that may increase emissions in the event of a malfunction. For example, OBD may monitor performance of the catalytic converter based on oxygen sensor signals. If a malfunction occurs, the OBD may set a diagnostic trouble code (DTC) to identify the malfunction so that the malfunction may be remedied. OBD may also notify a driver of the malfunction by displaying an indicator light.